Preparation of perfluoroaldehydes and aldehydrols



United States Patent ICE prises slowly adding a solution of lithium aluminum 569 hydride in a suitable solvent to a perfluorocarboxylic 2,852 acid, containing about 2-18 carbon atoms, to form an PREPARATION 0 PERFLUOROALDEHYDES intermediate or complex between the lithium aluminum AND ALDEHYDROLS hydride and the perfiuorocarboxylic acid, which is then Milton Braid, Philadelphia, and Francis Earl Lawlor, 32333 533 5? desired Perfiuomaldehydml by the ad- Wyndmoor, Pa, assignors to Pennsalt Chemicals Corpmafion a corporation of Pennsylvania About 0.25 to 1.0 mole of lithium aluminum hydride may be slowly added to 1.0 mole of a perfluorocarboxylic N0 Dlawlngpp June 1954 acid preferably dissolved in about one liter of solvent, Serial 434,333 maintained at a temperature of about l0 to +5 C., 6 Claims (CL 260 633) with the preferred temperature being in the range of about 5 to 0 C. The addition is accomphshed with constant a'tato and ab f ed e 'dfbut This invention relates to a novel method for the prep- 1 2 h or i rs or oi e. l l h e fie hgdri di scldiiion is co maration of perfluoroaldehydrols, which may be dehydrated pleted, the reaction mixture is agitated at a temperature in accordance with known procedures to produce perof about 0-S C. for about one hour and then hydrolyzed fluproaldehydest.h d f t fl tald h d with vgager and a suitagle acid, ngaigtainihglshectemjplerarevrous me o s or preparing r1 uoroace e y e ture o t emixture int orange 0 a out terinclude reduction of trifluoroacetonitrile With lithium 2O natively, the complex may be hydrolyzed immediately, but a luminn rrii hydridter followidlliylhtydirolysis and dehygraagi i altltinglfdog1 a: aldditio-nlalbperiod lot tirrie is preferred. b tron, 0x1 ative n1 ation o -r1 uoropropane, re uce a e y m is sou e in t e so vent an is 0 tion of trifluoroacetyl chloride with hydrogen and a Catatained, after hydrolysis, from the combined solvent layer 3311111.; fiifii fiofi ?$521133?ai diiiiii ii tfif iiiiily diifiiiii a.i iibi ii iyd fiil iltli tion. All of these procedures involve the laborious prepayields the free aldehyde. ration of intermediates and/or catalysts, with the excep- Among the solvents which may be employed in the tion of the last-named method. Poor overall yields of the process are diethyl ether, di-tertiary-butyl ether, tetradesired triiluoroacetaldehyde are obtained, and in the lasthydrofuran, and tetrahydropyran. Generally, any solvent named method the yield is about 25 percent. may be employed which is non-reactive with lithium In the prior art method for the reduction of perfluoroaluminum hydride and in which lithium aluminum hycarboxylic acids with lithium aluminum hydride, powdride is soluble at the temperature of reaction, this soludered lithium aluminum hydride is dissolved in a large bility being a controlling factor in the selection of a volume of diethyl ether, and to this solution 1s added, proper solvent. lDiethyl ether is the preferred solvent, dropwise, a solution of a perfluorocarboxylic acid 1n a due to the solubility of lltl'lllll'll aluminum hydride thereln diethyl ether solvent, while the reaction mixture is kept and the fluidity thereof at the reaction temperature. cool 1n an ice bath. The addition is made at a rate Which The aldehydrol may be dehydrated using a drying agent will produce a gentle reflux of the ether. The complex such as sulfuric acid, phosphorus pentoxide, or a mixture forgied tgetwleien1 the lihiun; alurnlilnum hydride1 anda1t1he 40 oilplciioilphlorus pentoxide and sulfuric acid, or other suitam is en y ro yze to orm e correspon mg 6- a e e y rating agent. hydrol from which the aldehyde may be recovered by The following table illustrates the advantage obtained dehydration, using a suitable drying agent. in adding the lithium aluminum hydride to the perfiuoro- In accordance with the present invention, it has been carboxylic acid rather than adding the acid to the anififi h y ir ri iifli ifviiiiiiifiififi cfiiififii ifii' ii iii? E; 32331??? if 2.131355??? the i e o 1 rum auminum tions of perfluorocarboxylic acids in suitable solvents hydride, the volume of ether solution added to the reprovides a convenient method for preparing perfluoroaction mixture, the reaction time and the total volume aldehydrols in substantially higher yields than have been of the reaction mixture are all decreased, while the yield obtained using the processes of the prior art. Only a of the aldehyde product is greatly increased, with nearly small quantity of 1,1:dlhYdIOP61'flll0IOfllCOhOl is obtained, three times as much product being obtained when the and the corresponding perfluoroaldehydes may be obmethod of the invention is employed.

TABLE 1 Moles Moles Vol. Ether Addition Total Aldehyde Method CFaCOOH LiAlH Soln. Time, Vol., Yield,

Added, rnl. hrs. ml. percent Acid to Hydride 1 1 ca. 2, 100 6 4, 600 26 Hydride to Acid l 0.57 750 1.5 1.750 77.5

1 Tabular values adjusted for 1 mole run.

tained by dehydration of the perfiuoroaldehydrols with a suitable drying agent. Only the stoichiometric amount of lithium aluminum hydride necessary for reduction of 6 The invention will be further illustrated by reference to the following specific examples in which all parts are by weight:

Example 1 114 parts (1 mole) of trifluoroacetic acid were dissolved in 708 parts of anhydrous diethyl ether and placed in a 3 liter flask equipped with a dropping funnel, a

nitrogen inlet, an agitator, a thermometer and a condenser protected by a soda-lime tube, followed by a mercury Patented Sept. 16, 1958' solved in 525 parts bubbler. The apparatus was flushed with nitrogen gas and cooled to a temperature of 5 C. with an ice-salt mixture. 21.5 parts of lithilun aluminum hydride (0.565 mole) dissolved in 525 parts of anhydrous diethyl ether were added to the flask, dropwise, over a period of 1 hour and 20 minutes, the temperature of the reaction mixture being maintained in the range of -3 C. during theaddition. Gas was evolved during the entire course of the addition, but ceased when the addition was completed. After completion of the addition, the reaction mixture was agitated at a temperature of 0 C. for 1 hour.

40 parts of water were then added to the flask over a period of 20 minutes, while passing nitrogen gas continuously through the flask and maintaining the temperature of the reaction mixture in the range of 0-5 C. and a mixture of 114.7 parts of concentrated sulfuric acid in 200 parts of water was then added over a period of 40 minutes at a temperature of 010 C. inorder to hydrolyze the lithium aluminum hydride-acid intermediate or complex.

Upon completion of this hydrolysis step, the ether solution suddenly became clear and some solid matter coagulated at the bottom of the flask. The ether'was decanted and 250 parts of water were added to the solids, which completely dissolved. This aqueous solution was extracted with four portions of ether (70 parts each) and the extracts were combined with the decanted ether. The ether was then removed by distillation at atmospheric pressure and a temperature of 80 C. through a short helix-packed column. The residue was primarily trifiuoroacetaldehydrol, 121.2 parts, and having a refractive index n =1.3339. The refractive index given in the literature is n =1.3404.

Example 2 Following the procedure of Example 1 above, 21.5 parts (0.565 mole) of lithium aluminum hydride, disof diethyl ether, were slowly added to 114 parts (1 mole) of trifluoroacetic acid, dissolved in 708 parts of anhydrous diethyl ether, over a period of 1 hour and 40 minutes at a temperature in the range of 1 to 2 C. The reaction mixture was then agitated for 1 hour at a temperature of C. and hydrolyzed at a temperature in the range of 0 C. to 5 C. with 40 parts of water, over a period of minutes, and a mixture of 114.7 parts of concentrated sulfuric acid and 200 parts of water over a period of minutes. At the completion of the hydrolysis step, the ether was decanted and the solid matter was dissolved in 300 parts of water and extracted four times with 125 part portions of ether.

Removal of the ether by distillation at a temperature of 85 C. produced a residue of crude trifluoroacetaldehydrol, 110 parts, and having a refractive index n 1.3323.

Example 3 6.5 parts of phosphoric anhydride and 55 parts of concentrated sulfuric acid were placed in a flask equipped with a dropping funnel, an agitator, a thermometer and a water-cooled condenser, followed by a solid carbon dioxide-acetone cooled cold trap protected by a drying tube. The flask was heated to a temperature of 85 C. and, while constantly agitating the contents of the flask, 15 parts of crude trifluoroacetaldehydrol (refractive index rz =1.3338) were dropped into the mixture over a period of 3 minutes, and the flask was then heated to a temperature of 125 C. The colorless vapor evolved was collected in the cold trap. The yield was 7.6 parts of the desired trifluoroacetaldehyde.

Example 4 Following the procedure of Example 3 above, parts-- 4 of the reaction of Example 2 above, were dehydrated and 34.5 parts of 2,2,2-trifluoroacetaldehyde were obtained, representing an overall yield of the aldehyde of 77.5%.

Example 5 Following the procedure of Example 1 above, a mixture of 11 parts of lithium aluminum hydride and 266 parts of anhydrous diethyl ether was slowly added to a mixture of 82 parts of perfluoropropionic acid and 354 parts of anhydrous diethyl at a temperature of 5 to 0 C. over a period of 1 hour and 10 minutes. The mixture was then stirred for 0.5 hour and hydrolyzed with water and sulfuric acid at a temperature of 3 to +5 C. Removal of the ether solvent after extraction of the reaction mixture produced a crude aldehydrol which was dehydrated with a mixture of P 0 and sulfuric acid to produce perfluoropropionaldehyde in a yield of 60.1%.

Example 6 Following the procedure of Example 1 above, a mixture of 11 parts of lithium aluminum hydride and 266 parts of anhydrous diethyl ether was added to a mixture of 112 parts of perfluorobutyric acid and 354 parts of anhydrous diethyl ether. The complex was hydrolyzed and extracted as before, and the perfluorobutyraldehydrol produced was dehydrated as before to produce perfluorobutyraldehyde in a yield of 64%.

The term perfluoroalkyl, as used herein, denotes the fiuoroalkyl group of the structure C F It will be obvious to those skilled in the art that many modifications may be made within the scope of the present invention without departing from the spirit thereof and the invention includes all such modifications.

We claim:

1. In a process for preparing an aldehydrol having the structure perfluoroalkyl group having about 1 to 17 carbon atoms, by reduction of an acid having the structure R COOH in which R is as defined above, the improvement that comprises slowly adding approximately a stoichiometric amount of lithium aluminum hydride to the acid, with agitation, employing as reaction medium a solvent which is non-reactive with lithium aluminum hydride and in which lithium aluminum hydride is soluble at the temperature of reaction.

2. In the process for preparing an aldehyde havingthe structure R CHO in which R is a perfluoroalkyl group having about 1 to 17 carbon atoms by reduction of an acid having the structure R COOH in which R is as defined above, the improvement that comprises slowly adding an approximately stoichiometric amount of lithium aluminum hydride to the acid with agitation, employing as reaction medium a solvent which is non-reactive with lithium aluminum hydride and in which lithium aluminum hydride is soluble at the temperature of reaction, thereafter hydrolyzing the reaction product by treatment with 'water, and thereafter dehydrating the resulting aldehydrol by treatment with a drying agent.

3. The process of claim 1 in which the acid is trifluoroacetic acid, the aldehydrol is trifluoroacetaldehydrol, and the solvent for both reactants is diethyl ether.

4. The process of claim 1 in which the acid is perin which R;- is a fluoropropionic acid, the aldehydrol is perfluoropropionaldehydrol, and the solvent ether.

5. The process of for both reactants is diethyl claim 1 in which the acid is perfluorobutyric acid, the aldehydrol-is perfluorobutyraldehydrol,

and the solvent for both reactants is diethyl ether.

6. The process of claim 2 in which the drying agent for the last step is a mixture of phosphorus pentoxide and sulfuric acid.

(References on following page) 5 6 References Cited in the file of this patent etc. (October 1947); J. Am. Chem. Soc., vol. 69, page UNIT 2548.

ED STATES PATENTS Hochstein at 211.: Addition of LiAlH to Double 2,568,500 Husted a1 Sew-18,1951 Bonds" (October 1948), J. Am. Chem. Soc., vol. 70, p. 2,666,797 Husted et a1 Jan. 19, 1954 5 3485 OTHER REFERENCES Gaylord: Reduction With Complex Metal Hydrides,

Nystrom et a1: Reduction of Organic Compounds, Interscience 101742 

1. IN A PROCESS FOR PREPARING AN ALDEHYDROL HAVING THE STRUCTURE 